1. Technical Field
The present invention relates to a fluid jet device for emitting a jet of a fluid at high speed, and in particular to a fluid jet device suitable for emitting a jet of a fluid in the condition of maintaining desired jet force.
2. Related Art
In the past, as a fluid jet device for incising or excising body tissue, there is known a device provided with a pulsation generation section having a fluid chamber with a variable capacity, an entrance channel and exit channel communicated to the fluid chamber, and a capacity varying section for varying the capacity of the fluid camber in response to supply of a drive signal, a connection channel having one end communicated to the exit channel and the other end provided with a fluid jet opening section (a nozzle) with a diameter smaller than that of the exit channel, a connection channel tube provided with the connection channel penetrating therethrough and having rigidity with which the pulsation of the fluid flowing from the fluid chamber can be transmitted to the fluid jet opening section, and a pressure generation section for supplying the entrance channel with the fluid, and for supplying the entrance channel with the fluid with the pressure generation section at a constant pressure, and at the same time varying the capacity of the fluid chamber with the capacity varying section to generate the pulsation, thereby performing ejection operation of the fluid (e.g., JP-A-2008-82202 (Document 1)).
According to the Document 1, a patent application by the inventors of the invention, in the case in which the capacity of the fluid chamber of a fluid jet device is not varied, the fluid flows through the fluid chamber in the condition in which the supply pressure by the pressure generation section (e.g., a pump) and the channel resistance balanced with each other. When shrinking the fluid chamber rapidly, the pressure in the fluid chamber rises. At that moment, since an increased amount of fluid ejected from the exit channel is larger than a decreased amount of flow volume of the fluid flowing from the entrance channel into the fluid chamber, a pulsation flow occurs in the connection channel. The pressure pulsation in the ejection operation propagates in the connection channel tube, and thus the fluid jet is emitted from the fluid jet opening section of the nozzle at the tip of the connection channel tube. The fluid chamber becomes in a vacuum state (0 atm or nearly 0 atm) immediately after the pressure rise due to the interaction between decrease in inflow volume of the fluid from the entrance channel and increase in outflow of the fluid from the exit channel. As a result, after predetermined time has elapsed due to both of the pressure of the pump and the vacuum state inside the fluid chamber, there is restored the flow of the fluid in the entrance channel towards the inside of the fluid chamber at the same speed as before the operation of the piezoelectric element.
In the technology of the related art described in the Document 1, although it is arranged that the capacity varying section configured including the piezoelectric element and a diaphragm is driven by a pulsed drive signal, in the case, for example, in which it is driven by a simple sinusoidal drive signal, the subsequent capacity reduction operation (compressing operation) might be performed before the flow proceeding toward the inside of the fluid chamber is restored to the steady state. If the subsequent compressing operation is performed before restoring the steady state, it is not achievable to obtain sufficiently strong jet force (jet).